The present invention relates to a dielectric fluid system of an electric discharge machining apparatus for collecting dielectric fluid from a work tank of the electric discharge machining apparatus cleaning the fluid and re-supplying the fluid to the work tank.
Electric discharge machining is a process for machining a workpiece into a desired shape by periodically applying an appropriate electric discharge machining voltage between the workpiece and a tool electrode (hereafter referred to simply as an electrode) arranged opposite to each other across a specified electric discharge machining gap (hereafter referred to simply as the machining gap) to continuously generate electric discharges, and moving the workpiece and the tool electrode relative to each other. In order to be better able to carry out this electric discharge machining process, electric discharge machining fluid (hereafter referred to simply as dielectric fluid) is supplied to the machining gap.
The dielectric fluid plays several important roles as a machining medium for electric discharge machining. A first role is to remove chips and debris generated as a result of electric discharges from the machining gap, as well as tar-like products which may become entrained in some dielectric fluids as a result of the heat due to the electric discharges. A second role is to cool the machining gap so as to create favorable conditions for the electric discharge machining process, and to suppress the tendency for deformation of the workpiece due to thermal expansion. A third role is to maintain isolation of the machining gap in order to maintain favorable electric discharge machining conditions. As will be described below, when an aqueous dielectric fluid is used, the specific resistance of water is usually adjusted.
Therefore, the dielectric fluid used for electric discharge machining in the work tank is filtered, cooled and subjected to specific resistance adjustment as required, and then re-supplied to the work tank after being collected in a dielectric fluid reservoir. Where an electric discharge machine uses a flushing device such as a flushing nozzle, dielectric fluid is similarly supplied to a machining gap after being filtered. A typical electric discharge machining apparatus is therefore provided with a dielectric fluid system for supplying and controlling dielectric fluid.
A typical dielectric fluid system includes a dielectric fluid reservoir having a dirty dielectric fluid tank and a clean dielectric fluid tank. Dirty dielectric fluid that has been discharged from the work tank is temporarily collected in the dirty dielectric fluid tank, and chips and debris having a comparatively heavy specific gravity precipitate here. The dielectric fluid in the dirty fluid tank is pumped through a filter apparatus by a pump, and chips and debris in the fluid are removed from the fluid which is then stored in the clean dielectric fluid tank. Decontaminated dielectric fluid in the clean fluid tank is re-supplied to the work tank by a pump, and supplied to the machining gap for flushing, as required.
This type of dielectric fluid system may also include a dielectric fluid cooling apparatus, for keeping the dielectric fluid in the work tank at a specified temperature. Also, a dielectric fluid system of an electric discharge machining apparatus which uses water based dielectric fluid may be provided with, for example, a specific resistance control apparatus including a deionizer using mixed-bed resin, which regulates the specific resistance of the dielectric fluid so as to maintain it at a value within a specified range.
The above-described conventional dielectric fluid system has several short commings which the present invention is intended to overcome.
A first object of the present invention is to reduce the time for supplying dielectric fluid to an empty work tank (hereafter referred to as rapid feed), and more specifically to shorten the rapid feed time. Conventionally, when submerging a workpiece in dielectric fluid to perform electric discharge machining, the amount of dielectric fluid to be supplied to the work tank is comparatively large, and the waiting time until the work tank is filled is too long. Accordingly, an apparatus has been proposed to supply dielectric fluid to the clean dielectric fluid tank having a large capacity matching the work tank, arranged at a position higher up than the work tank, thus supplying the dielectric fluid to the empty work tank in a reduced amount of time. This is disclosed, for example, in Japanese laid open Patent No. Hei. 5-004117 and Japanese laid open Patent No. Hei. 5-042424.
A second object of the present invention is to reduce the installation space occupied by an electric discharge machining apparatus. Conventionally, in those electric discharge machining apparatus in which the workpiece is submerged in a dielectric fluid for machining, in order to replace the workpiece after machining it is necessary to temporarily store the dielectric fluid which is in the work tank in a dirty dielectric fluid tank having a capacity matching the volume of the work tank. Also, in order to supply cleaned dielectric fluid to the empty work tank in a reduced time, it is also necessary to store, in the clean dielectric fluid tank, a volume of clean dielectric fluid which matches the volume of the work tank. As a result, the capacity of the dielectric fluid reservoirs for both the dirty dielectric fluid tank and the clean dielectric fluid tank is from 2.5 to 3.0 times the capacity of the work tank. This gives rise to a problem in that the installation space required by the dielectric fluid system is quite large compared to the overall installation space of the electric discharge machining apparatus. As a countermeasure in order to reduce the installation space of the storage tank, the height of the storage tank is increased or the dirty dielectric fluid tank and the clean dielectric fluid tank are arranged so as to have a two-stage overlapping structure. This is disclosed, for example, in Japanese laid open Patent No. Hei. 4-171123.
A third object of the present invention is to efficiently perform collection and filtration of some of the dielectric fluid in the work tank, and return it to the work tank during electric discharge machining (hereafter referred to as circulation). Conventionally, when the dielectric fluid reservoir is provided with a dirty dielectric fluid tank and a clean dielectric fluid tank, some of the dielectric fluid in the work tank is collected in the dirty dielectric fluid tank, is filtered by being passed through a filter, and is temporarily stored in the clean dielectric fluid tank. Then, dielectric fluid in the clean dielectric fluid tank is circulated by being re-supplied to the work tank. In this case, as preparation for feeding clean dielectric fluid to the empty work tank at the time of commencing the subsequent electric discharge machining operation, it is necessary to store a large volume of dielectric fluid, significantly more than the amount of dielectric fluid required for circulation, in the clean dielectric fluid tank during the preceding electric discharge machining operation. For this reason, a pump having a large discharge capacity and a filtration device for filtering a large volume are required, thus increasing costs. Also, particularly when water based dielectric fluid is used, the dielectric fluid comes into contact with more air while being stored in the large fluid tank, and there is a problem that the specific resistance value is reduced due to carbon dioxide penetration, etc. As a countermeasure, it has been considered to directly collect dielectric fluid overflowing while performing electric discharge machining using a pump, filtering using a filter, and to return the fluid directly to the work tank. This is disclosed, for example, in publications such as Japanese laid open Patent No. Hei. 5-037422, Japanese laid open Patent No. 8-215940 and Japanese Utility Model No. 2557992.
As described above, there are various problems in existing dielectric fluid systems which require improvement and solutions to some of these problems have been considered. However, none of the solutions proposed to date are adequate for solving all of the above-mentioned problems. It is desirable to provide a dielectric fluid system which minimizes the installation space occupied by a dielectric fluid tank, efficiently filters and circulates dielectric fluid to supply clean dielectric fluid quickly to the work tank, and wherein, even if there is trouble with the pump of the supply device or clogging of the filter no major damage to the dielectric fluid supply system will result.
It is therefore an object of the present invention to provide an improved dielectric fluid system for an electric discharge machine that has a relatively small installation space, and also reduces the time for feeding dielectric fluid to an empty work tank and that efficiently filters dielectric fluid circulating during electric discharge machining.
It is also an object of the present invention to provide a dielectric fluid system for an electric discharge apparatus which implements safety measures to avoid major failures.
These and other objects and advantages of the present invention are achieved by the dielectric fluid system described below.
According to the present invention, a dielectric fluid system for an electric discharge machining apparatus, for supplying dielectric fluid to a work tank with a workpiece submerged in the dielectric fluid may comprise a dielectric fluid reservoir for storing dielectric fluid collected from the work tank, an auxiliary tank positioned higher than the work tank and positioned at or above the height of the dielectric fluid reservoir, a filter device arranged between the dielectric fluid reservoir and the auxiliary tank, a main supply pipe line connecting the dielectric fluid reservoir to the auxiliary tank, and, provided in series with a first pump, a filter device and a second pump, a circulating pipe line connected to the main supply pipe line at an intake side of the first pump and branching from the main supply pipe line at an outlet side of the second pump and connecting to the work tank, a rapid feed pipe line having a first drain valve for connecting from the auxiliary tank to the work tank, a drain pipe line having a second drain valve for connecting the work tank to the dielectric fluid reservoir, first and second control valves positioned at an intake side of the first pump for selectively connecting the main supply pipe line and the circulating pipe line, and third and fourth control valves positioned at an outlet side of the second pump for selectively connecting the main supply pipe line and the circulating pipe line.
With this structure, clean dielectric fluid may be temporarily stored in the compact filter device and the auxiliary tank arranged at or above the height of the dirty dielectric fluid tank. This which means that there is no need for a large, clean dielectric fluid tank as in the related art. During advance preparation etc., dielectric fluid may be pumped to the auxiliary tank which is arranged at a position at or above the top of the work tank, and when the dielectric fluid is fed to the work tank, the dielectric fluid falls quickly from the auxiliary tank to the work tank and at the same time deficient dielectric fluid, to the extent there is any in the auxiliary tank, is pumped from the dielectric fluid reservoir to the auxiliary tank. This means that the time needed to feed dielectric fluid to the work tank is effectively only the time needed to pump the deficient dielectric fluid to the auxiliary tank, thus further reducing the feed time.
A dielectric fluid system of an electric discharge machining apparatus of the present invention may further be provided with a flushing pipe line branching from the circulating pipe line at an outlet side of the second pump and connecting to a flushing device of the electric discharge machining apparatus, and provided with a third pump and a fifth control valve group inside the flushing pipe line for selectively opening and closing the flushing pipe line.
With this structure, a flushing operation in which dielectric fluid is collected from the work tank, filtered, and jetted into the machining gap may be efficiently carried out by directly circulating a minimum amount of dielectric fluid.
A dielectric fluid system of an electric discharge machining apparatus of the present invention may further be provided with a by-pass pipe line, branching from the main supply pipe line at an intake side of the first pump, for connecting the flushing pipe line which includes the third pump, at an intake side of the third pump, branching from the flushing pipe line at an outlet side of the third pump and connecting to the auxiliary tank, and a sixth control valve for selectively opening and closing the by-pass pipe line.
With this structure, when the dielectric fluid system pumps dielectric fluid to the auxiliary tank, it is possible to use the third pump of the flushing pipe line in addition to the main supply pipe line pump, which means that the rapid feed of dielectric fluid to the work tank can be made still shorter.
Either of the dielectric fluid systems for an electric discharge machining apparatus according to the present invention may be further provided with a relief pipe line, including a relief valve, connecting an upstream side and a downstream side of the filter device and arranged in parallel with the filter device, and a regulating pipe line connecting a branch point at an intake side of the first pump to a confluence point at an intake side of the second pump, the confluence point being downstream of the filter device, and arranged in parallel with the first pump and the filter device.
In this way, because the relief pipe line of the dielectric fluid system is in parallel with the filter device and the regulating pipe line is in parallel with the first pump and the filter device, the first and second pumps do not require an extremely large discharge capacity. In addition, even if the filter device becomes clogged, the filter will not rupture, and even if there is a failure of one of the pumps, there will be no overall pump failure.